DIFFERENTIAL GEARBOX FOR A MOTOR VEHICLE

Description

[0001] The invention relates to a differential gear for a motor vehicle according to the type specified in the preamble of patent claim 1.

[0002] Differential gears and various concepts for mounting the final drive gear on the differential housing are well known in the art. Reference is made to EP 2 740 562 B1, DE 10 2017 006 417 A1, and DE 10 2016 218 087 A1 as examples. In particular, the axial forces introduced via the gear teeth of the final drive gear can lead to "tilting" and thus to a displacement of the gear teeth, which in turn causes less favorable tooth contact and thus uneven motion transmission (speed, torque). The uneven motion transmission results in acoustic abnormalities, which in turn can be the cause of vehicle complaints. These acoustic complaints are becoming increasingly important, particularly with regard to new vehicle concepts featuring electric drive.

[0003] DE 10 2011 087 579 A1 discloses a spur gear differential for a drive train of a motor vehicle, comprising a planetary carrier in which two sun gears, each with external toothing, are arranged, each meshing with a differential gear configured as a planetary gear. The two planetary gears are in positive engagement with one another. Furthermore, there is an axle drive gear arranged substantially radially outside the planetary carrier. Between an inner surface of the axle drive gear and a radial circumferential surface of the planetary carrier, a torque-transmitting connection is provided, which is configured as a material-fit, form-fit, force-fit, interference fit, caulked fit, and / or welded joint.

[0004] From US 2017 / 0 219 077 A1 a generic differential for a motor vehicle with the features of the preamble of claim 1 is known.

[0005] The invention is based on the object of developing a differential gear according to the type specified in the preamble of patent claim 1 in such a way that the undesired displacement of the teeth is prevented and thus the risk of acoustic abnormalities occurring during operation is reduced.

[0006] This problem is solved by the characterizing features of patent claim 1 in conjunction with its preamble features.

[0007] The subclaims form advantageous developments of the invention.

[0008] In a known manner, the differential gear comprises a rotatably mounted differential housing and an axle output gear mounted on the differential housing in a rotationally fixed manner and having an external toothing, which in turn meshes with and is driven by an associated drive shaft via its external toothing.

[0009] In addition, the differential housing has two fitting surfaces on its outer circumferential surface and the axle driven gear has two corresponding, radially opposite fitting surfaces on its inner circumferential surface. For the sake of completeness, it should be noted that the fitting surfaces formed on the differential housing and on the axle driven gear are designed as circumferential fitting surfaces. The fitting surfaces on the outer circumferential surface of the differential housing and those on the inner circumferential surface of the axle driven gear are each designed as separate fitting surfaces, viewed in the axial direction, arranged geometrically apart from one another at a distance A. The axle driven gear is pressed onto the differential housing so that the axle driven gear and the differential housing are connected to one another by means of a first press fit and a separate second press fit axially spaced at a distance A.

[0010] The two separate press fits, axially spaced at a distance A, provide an extremely rigid bearing arrangement. This ensures that all forces resulting from the gearing can be absorbed by the rigid bearing arrangement. The tendency to tilt is significantly reduced, ensuring optimal tooth contact and thus a uniform motion transmission that does not cause unwanted noise.

[0011] According to the invention, both the mating surfaces formed on the outer circumferential surface of the differential housing and the mating surfaces formed on the inner circumferential surface of the axle drive gear are each separated from one another in the axial direction by a circumferential groove formed in the respective circumferential surface, wherein the grooves each have a length corresponding to the distance A when viewed in the axial direction. The groove ensures an easy-to-produce, effective geometric separation of the mating surfaces and thus the press fit. A further advantage is that the material removal caused by the groove has a positive effect on the component weight, thus enabling a particularly weight-optimized design. By appropriately dimensioning the groove depth, the material removal and thus the weight savings can be easily influenced.

[0012] The grooves preferably have a rectangular, triangular or semicircular basic shape.

[0013] To ensure a sufficiently rigid bearing, the distance A between the mating surfaces should be as large as possible. Initial tests have shown that the desired effect, namely the rigid bearing, is ensured if 0,5 ≤ A / L ≤ 0,7 , where L is the axial length of the inner circumferential surface of the axle driven gear viewed in the axial direction.

[0014] The differential gear according to the invention is characterized by the fact that the two press fits have a small radial overlap of 10 to 50 µm and that an additional positive connection is formed between the axle drive gear and the differential housing. The advantage of this is that, due to the relatively small radial overlap, the two components are easy to join, and, moreover, the additional positive connection ensures high torque transmission.

[0015] According to the invention, the additional connection is designed in the form of a polygonal or spline toothing, with a locking element arranged between the axle drive gear and the differential housing to prevent relative movement in the axial direction. The advantage of this design is that, due to the positive connection, it has a low component weight compared to a material connection.

[0016] The securing element is preferably designed in the form of a securing ring, in particular in the form of a wedge-shaped securing ring.

[0017] Preferably, the differential housing is made of cast iron and the axle output gear is made of a hardenable material.

[0018] Further advantages and possible applications of the present invention will become apparent from the following description in conjunction with the embodiment shown in the drawing.

[0019] In the drawing: Fig. 1 a sectional view of an embodiment of a differential gear according to the invention; Fig. 2 the differential gear from Fig. 1 in plan view; Fig. 3 a first comparative form not covered by the invention in sectional view; Fig. 4 the differential gear from Fig. 3in plan view; Fig. 5 a sectional view of a second comparative form not covered by the invention, and Fig. 6 the differential gear from Fig. 5 in the top view.

[0020] In the following description and in the figures, to avoid repetition, identical parts and components are marked with the same reference symbols unless further differentiation is necessary or useful.

[0021] Fig. 1 and 2 show an embodiment according to the invention of a differential gear of a motor vehicle, designated overall by the reference number 10.

[0022] The differential gear 10 comprises a differential housing 12 and an axle output gear 14 which is connected in a rotationally fixed manner to the differential housing 12. The axle output gear 14 is operatively connected via its external toothing 14-1 to a drive shaft (not shown here for reasons of clarity).

[0023] Via a cross-shaped driving pin 16, the differential housing 12 drives four planetary gears 18, which in turn mesh with two output gears 20, which can be connected in a rotationally fixed manner to gear shaft axes - not shown here for reasons of clarity.

[0024] How Fig. 1 and 2 As can be seen, the differential housing 12 has two fitting surfaces on its outer circumferential surface and the axle drive gear 14 has two radially opposite fitting surfaces on its inner circumferential surface, which are each designed as separate fitting surfaces viewed in the axial direction a, arranged geometrically separated from one another at a distance A, so that the axle drive gear 14 pressed onto the differential housing 12 is connected to one another by means of a first press fit 22-1 and a second press fit 22-2 which is separate therefrom and axially spaced at a distance A.

[0025] In order to ensure sufficient spacing between the press fits 22-1 and 22-2 for tilt-resistant mounting, the distance A must be selected such that: 0,5 ≤ A / L ≤ 0,7 , where L denotes the axial length of the inner circumferential surface of the axle drive gear 14 viewed in the axial direction a.

[0026] For the geometric separation of the fitting surfaces and thus the first and second press fit 22-1, 22-2, as Fig. 1 As can be seen further, a groove 24 is milled into the circumferential surface of the differential housing 12 and into the circumferential surface of the axle drive gear 14. In addition to the geometric separation, the grooves 24 also advantageously result in a weight reduction.

[0027] In the present case, the introduced grooves 24 each have a substantially rectangular basic shape.

[0028] Due to the arrangement of the two press fits 22-1, 22-2 spaced apart in the axial direction a, an extremely tilt-resistant bearing is provided which can absorb all axial forces resulting from the meshing of the external toothing 14-1 of the axle output gear 14 with a drive shaft (not shown here), so that optimal tooth contact and thus a uniform movement transmission which does not cause undesirable noise is ensured.

[0029] According to the Fig. 1 and Fig. 2 In the illustrated embodiment, the two press fits 22-1 and 22-2 have a radial overlap of 10 to 50 µm. To ensure torque transmission, an additional positive connection is formed between the axle drive gear 14 and the differential housing 12 in the area of ​​the first press fit 22-1. Axial locking is ensured by a retaining ring 26.

[0030] As is particularly evident from Fig. 2As can be seen, the positive connection is designed in the form of a polygonal toothing 28.

[0031] The Figs. 3 and 4 The first comparative form shown and not covered by the invention essentially corresponds to the one shown in Fig. 1 and 2 illustrated embodiment of the invention. Compared to the embodiment of the invention, this comparative form differs in that the additional connection between the axle drive gear 14 and the differential housing 12, which serves to transmit torque, is designed in the form of a welded connection 30. As is particularly Figs. 3 and 4 show - the welded joint 30 is formed as a one-sided, circumferential weld seam layer located only in the area of ​​the first press fit 22-1. In addition to torque transmission, the weld also ensures axial fixation.

[0032] The Figs. 5 and 6The comparative form shown, which is not encompassed by the invention, differs from the embodiment according to the invention in that, instead of a positive connection, a force-locking connection is now provided exclusively for torque transmission. To ensure sufficient torque transmission, the two press fits 22-1, 22-2 have a radial overlap of >200 µm.

Claims

1. Differential gear (10), comprising a rotatably mounted differential housing (12) and a final drive gear (14) mounted for conjoint rotation with the differential housing (12), wherein the differential housing (12) has two mating surfaces on its outer circumferential surface and the final drive gear (14) has two radially opposite mating surfaces on its inner circumferential surface, wherein the mating surfaces formed on the outer circumferential surface of the differential housing (12) and the mating surfaces formed on the inner circumferential surface of the final drive gear (14) are each designed as mating surfaces which are separate, as viewed in the axial direction (a), and are geometrically separated from one another at a distance (A), and wherein the final drive gear (14) is pressed onto the differential housing (12) such that the final drive gear (14) and the differential housing (12) are connected to each other by means of a first press fit (22-1) and a second press fit (22-2) which is separate therefrom and axially spaced at a distance (A), characterized in that the mating surfaces formed on the outer circumferential surface of the differential housing (12) and the mating surfaces formed on the inner circumferential surface of the final drive gear (14) are separated from each other in the axial direction (a) in each case by a circumferential groove (24) introduced into the respective circumferential surface, wherein the grooves (24), as viewed in the axial direction (a), each have a length corresponding to the distance (A), in that the two press fits (22-1, 22-2) have a radial overlap of 10 to 50 µm, in that an additional formfitting connection is formed between the final drive gear (14) and the differential housing (12), and in that the additional connection is in the form of a polygonal toothing or mating toothing (28), and in that a securing element (26) preventing a relative movement in the axial direction (a) is arranged between the final drive gear (14) and the differential housing (12).

2. Differential gear (10) according to Claim 1, characterized in that the grooves (24) have a rectangular, triangular or semi-circular basic shape.

3. Differential gear (10) according to either of Claims 1 and 2, characterized in that, as viewed in the axial direction (a), the inner circumferential surface of the final drive gear (14) has a length (L), and in that, in relation to the length (L) of the inner circumferential surface, the following applies for the distance (A) between the mating surfaces: 0.5 ≤ A / L ≤ 0.7 .

4. Differential gear (10) according to any one of the preceding claims, characterized in that the securing element (26) is formed in the form of a securing ring.

5. Differential gear (10) according to any one of the preceding claims, characterized in that the differential housing (12) is made of cast iron and the final drive gear (14) is made of a curable material.